How to identify Orbicular Jasper

To correctly identify Orbicular Jasper (Orbicular Jasper (a variety of Chalcedony/Microcrystalline Quartz)), check each of these features in order. Many rocks and minerals look alike, so cross-reference multiple properties before deciding.

Step-by-step identification

1. 1

   Color

   Overall color and any zoning or banding

   Highly variable, including shades of green, red, brown, yellow, gray, white, and black. The key is the presence of distinct, often contrasting, orbicular patterns.

2. 2

   Luster

   How the surface reflects light: metallic, vitreous, dull

   Dull to waxy or vitreous when polished.

3. 3

   Texture

   Grain size and surface feel: coarse, fine, glassy

   Microcrystalline, dense, and fine-grained. The surface can feel smooth when polished.

4. 4

   Crystal Form

   Shape of visible crystals or crystal faces

   Massive, cryptocrystalline aggregates. Individual quartz crystals are microscopic and not visible to the naked eye.

5. 5

   Cleavage

   How it breaks: flat cleavage planes vs irregular fracture

   None, due to its microcrystalline nature.

6. 6

   Geological Environment

   The rock formation and setting where it occurs

   Typically found in association with volcanic rocks (e.g., rhyolite, basalt) where silica-rich fluids have permeated and filled voids or fractures. Also found in sedimentary environments where silica has replaced other minerals or filled concretions. Often occurs in hydrothermal alteration zones.

Key Facts

Hardness

6.5-7 on the Mohs scale (due to its quartz composition).

Specific Gravity

2.58-2.91 g/cm³ (varies slightly with impurities).

Crystal System

Trigonal (for the constituent quartz crystals, but macroscopically amorphous/cryptocrystalline).

Color

Extremely varied, often with multiple colors in a single specimen, characterized by orbicular patterns.

Luster

Dull, waxy, or vitreous (when polished).

Transparency

Opaque.

Fracture

Conchoidal to splintery.

Cleavage

None.

Composition

Silicon dioxide (SiO2) with varying amounts of iron oxides (hematite, goethite), clay minerals, chlorite, and other mineral inclusions that create the color and patterns.

Physical characteristics

• Crystal Habit: Massive, cryptocrystalline aggregates, forming nodules, veins, or fillings.
• Cleavage Type: None.
• Fracture Type: Conchoidal to splintery, typical of microcrystalline quartz.
• Tenacity: Brittle.
• Luster Type: Dull to waxy, sometimes vitreous on polished surfaces.

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